This chemistry question involves key chemical concepts and calculations. The detailed solution below walks through each step, from identifying the reaction type to computing the final answer.
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You're on a roll — The octane number of petrol is a measure of its resistance to knocking or pre-ignition in an internal combustion engine. A higher octane number indicates better fuel quality and less knocking. The octane number is influenced by the structure of the hydrocarbon molecules: Straight-chain alkanes have low octane numbers and are prone to knocking. Branched-chain alkanes have higher octane numbers and are more resistant to knocking. The more highly branched an alkane is, the higher its octane number. Let's analyze the given options: A) 2,4-dimethylpentane: This is a branched alkane with a 5-carbon main chain and two methyl branches. B) 2,2,4-trimethylpentane: This is a highly branched alkane with a 5-carbon main chain and three methyl branches. This compound is also known as isooctane and is assigned an octane rating of 100, serving as the reference standard for octane numbers. C) Octane (n-octane): This is a straight-chain alkane with 8 carbons. Straight-chain alkanes have very low octane numbers. D) 2-methylpentane: This is a branched alkane with a 5-carbon main chain and one methyl branch. Comparing the degree of branching: n-octane (C) has no branches. 2-methylpentane (D) has one branch. 2,4-dimethylpentane (A) has two branches. 2,2,4-trimethylpentane (B) has three branches. Since 2,2,4-trimethylpentane is the most highly branched alkane among the options, it will have the highest octane number. The final answer is B. What's next?